Primary Ovarian Insufficiency (POI) is a spectrum of disorders of early ovarian aging characterized by elevated follicle stimulating hormone (FSH) levels ranging from Diminished Ovarian Reserve (DOR, FSH > 10 mIU/mL and regular menses) to premature ovarian failure (POF, FSH > 40 mIU/mL and amenorrhea before age 40). The Genetics Committee of the American College of Obstetricians and Gynecologists and the American College for Medical Genetics (ACMG) have recommended genetic counseling and fragile X premutation (defined as ~55 - 200 CGG repeats in the FMR1 gene) screening for women with POI. While it is known that 5% of women with POF have a fragile X premutation, little is known about the CGG repeat count in women with DOR. Our preliminary data in 65 women with DOR and one published report (Streuli et al) in 27 women with POI (POF excluded) suggest that CGG repeats of 35-44 are markedly over-represented in women with this phenotype (14-17% prevalence). Current clinical guidelines state that an FMR1 CGG repeat count < 45 is not associated with an abnormal phenotype; however our data and that from Streuli suggest that this is incorrect, and that indeed there is an infertility phenotype associated with 35-44 triplet repeats. The proposed study, in direct response to the NIH Research Plan on Fragile X Syndrome and Associated Disorders Objectives 1.4 and 3.1, seeks to substantiate the association between the FMR1 triplet repeat count and this infertility phenotype. This study will compare the CGG repeat count in a cohort of 110 DOR cases with 2 comparison cohorts (680 women with proven fertility and normal ovarian aging defined by natural menopause over age 45 participating in the Study of Women's Health Across the Nation (SWAN), and 170 women who are infertile due to an anatomical reason such as tubal occlusion). DNA samples from the SWAN cohort have already been collected. The second comparison group will be recruited through this grant. The specific aims are to (1) determine if the proportion women with 35-44, 45-54 and >55 FMR1 CGG repeats is greater in subjects with DOR than in the 2 comparison groups, (2) estimate the optimal threshold of CGG repeats for an elevated risk of DOR, and (3) characterize the CGG repeat distribution and potential modifiers in these phenotypically distinct cohorts. The comparisons cohorts will provide critical information to distinguish whether DOR is a new phenotype associated with the FMR1 gene and will provide data with which to disentangle the potential separate mechanistic influences on infertility and ovarian aging. Data acquired by the proposed studies will clarify the effects of allele size on fertility (e.g., reduced reproductive window) and therefore can be used clinically to provide medical guidance for individual decision-making by reproductive age women with POI and their female offspring. Our findings are anticipated to challenge the interpretation of the current FMR1 CGG reference range, which is based on the diagnosis of Fragile X Syndrome in children and their premutation carrier parents, and may not be appropriate for screening adult females with POI.